1. Field of the Invention
The present invention relates to a treatment method for annealing and/or doping of semiconductor.
2. Description of the Prior Art
A large scale semiconductor integrated circuit (referred to as “LSI” hereinafter) is manufactured by means of many processes, for example, a process of forming thin films made of various sorts of materials, a photolithographic process of processing a film made of a semiconductor and a film made of others to form each film in a certain shape, a process of adding an impurity (referred to as “dopant” hereinafter) to the semiconductor (referred to as “doping” hereinafter), a dopant activation process for electrically activating the dopant inside the semiconductor, and so forth.
An ion doping method is well known as a typical method of adding a dopant used in the above doping process. This method ionizes a specific impurity and dopes a semiconductor crystal with a certain amount of the above ionized impurity. Furthermore, this method has an advantage in that the concentration distribution and diffusion depth of the dopant can be controlled with high accuracy and good reproducibility. In order to repair the defect in crystalline structure which is caused by this ion doping and also to activate the dopant as doped, the above semiconductor is heat-treated in a heat treatment furnace for annealing, which is generally kept at a temperature exceeding 1000° C. (referred to as “process temperature” hereinafter).
In recent years, in association with the process of manufacturing a device constituting the LSI, for example, a metal-oxide-semiconductor (referred to as “MOS” hereinafter) transistor provided with an extremely shallow junction having several tens nm thickness or less, there is studied a laser anneal method as a method of activating the dopant, which is performed after the semiconductor is doped therewith by means of the ion doping method.
In the field of the liquid crystal display (referred to as “LCD” hereinafter), the thin film transistor (referred to as “TFT” hereinafter) including a semiconductor thin film formed on an insulator, is used mainly as a switching device controlling the voltage applied to respective pixels of the LCD.
In order to realize reducing the cost of the LCD, enlarging the display panel area of the LCD, and providing a high performance LCD, and so forth, there has been made every effort to develop a new method enabling a high performance TFT to be manufactured at a process temperature (600° C. or less), which is lower than the prior process temperature of 1000° C.
In the process of manufacturing the high performance TFT, the laser anneal method is used for forming a thin film made of amorphous silicon (referred to as “a-Si” hereinafter) on an insulating film formed directly or indirectly on a substrate, and irradiating the a-Si thin film with the laser beam to melt and crystallize (mainly poly-crystallize) at least a part of the above a-Si thin film. This method has following merits. One is that as a thin film made of a low temperature poly-silicon (referred to as “p-Si” hereinafter) is formed, the substrate on which the above thin film is directly or indirectly formed is less affected thermally, the second is that the high throughput can be realized, and the third is that the inexpensive glass substrate, plastic base plate and others may be utilized.
In the process of manufacturing the TFT, this laser anneal method may be actively used not only for changing the crystalline state from a-Si to p-Si, but also for annealing the dopant after finishing the doping process.
FIG. 7 is a flow chart for roughly showing a prior art steps of manufacturing a semiconductor device by way of an example of a TFT manufacturing method using the ion doping method as well as the laser anneal method (see the following patent document 1).
Patent Document 1: JP Patent Public Disclosure 8-51207
Patent Document 2: JP Patent Publication 2002-122881
These documents describe that it is necessary to activate the dopant by the laser anneal after performing the doping of the dopant ion, thus increasing the number of manufacturing steps.
As shown in FIG. 7(a), after forming the a-Si film 22 on an insulating substrate 21, the a-Si film 22 is doped with the n-type dopant (c) such as phosphorus to make the a-Si film 22 an n-type a-Si film 30 (FIG. 7(b)) (channel doping).
As shown in FIG. 7(b), the n-type a-Si film 30 is annealed by using an irradiation by laser beam (a) from an excimer laser system, thereby melting and crystallizing (or recrystallizing) the n-type a-Si film 30 to change it into an n-type p-Si film (not shown).
In the next, as shown in FIGS. 7(c) to 7(e), in order to form a plurality of TFT devices, the n-type p-Si film is processed to form a plurality of island shaped n-type p-Si layers 31, a gate oxide film 23 is formed to cover the insulating substrate 21 and n-type p-Si layer 31, and then, a gate electrode 24 is formed on the gate oxide film 23 according to a certain pattern form.
As shown in FIG. 7(f), the doping of the n-type dopant (c) such as phosphorus is performed by making use of the gate electrode 24 as a protective mask against doping the dopant to form source and drain regions of the TFT. In this way, there is formed the principal portion of a depression type n-channel MOS transistor, of which the source and drain regions contact with each other through an n-type channel layer.
As shown in FIG. 7(g), with laser-annealing process by using an irradiation by laser beam (a) from the excimer laser system, the dopant as ion-doped is activated, and the crystal damage in the p-Si film caused by the ion doping is recovered.
After this step, as shown in FIG. 7(h), a passivation film 25 such as made of silicon oxide, is formed on the top of the above structure. Still further, as shown in FIG. 7(i), the above passivation film 25 is processed to form necessary contact holes in the above passivation film 25 and then, metal leads 26 for electrodes use are formed. With the manufacturing steps as described in the above, the semiconductor device is manufactured.
In the above conventional process for manufacturing the semiconductor device, however, the step of doping of the dopant and the step of laser anneal are separated from each other by a step or steps intervening between them. Because of this, the number of manufacturing steps was increased and works were unnecessarily complicated.
If the equipment for each of the step of doping the dopant and the step of laser anneal has to be separately prepared, some inconvenient situations come out. For example, it is required to carry out the substrate cleaning in each of the above separate equipments; the inside of each equipment is easily contaminated due to the substrate cleaning carried out before and after the step of the doping; and further, it was highly risky because a poisonous gas source was generally used in the doping equipment, so it required large scale additional facilities in order to eliminate the danger.